feat(D.5.3a): selected-object meter — Health bar + name on the action bar

Port of gmToolbarUI::HandleSelectionChanged (acclient_2013_pseudo_c.txt:198635).
When the player selects a world object the action bar's bottom strip shows the
object name + (for player/pet/attackable targets) a live Health meter; deselect
clears it. Mana (#140) + stack slider deferred.

- SelectedObjectController (new): clear-then-populate on selection change; sets
  name (UiText child, VitalsController pattern), overlay state (ObjectSelected /
  StackedItemSelected via UiDatElement.ActiveState), shows the health meter and
  sends QueryHealth for health targets. Subscribes via a delegate seam (no
  GameWindow coupling).
- GameWindow: _selectedGuid field -> SelectedGuid property + SelectionChanged
  event (fires on actual change only); 3 write sites converted, reads untouched.
  All selection-write paths (LMB pick, Tab/Q, despawn-clear via Tick()) run on
  the render thread, so the event-driven UI mutation is single-threaded.
- WorldSession.SendQueryHealth (0x01BF) — wraps SocialActions.BuildQueryHealth.
- DatWidgetFactory.BuildMeter: handle the single-image toolbar meter shape
  (back-track on the element's own DirectState, fill on one Type-3 child). The
  sprites go in the TILE slot (DrawMode=Normal tiles to full bar geometry per
  UIElement_Meter::DrawChildren) — a left-cap assignment would gap/clamp a
  sub-140px sprite. Vitals 3-slice path unchanged.
- ToolbarController.HiddenIds: A1 (health) now owned by SelectedObjectController;
  A2 (mana) + A4 (stack) stay hidden (deferred) so their dat back-tracks don't
  render as stray empty bars.

Adversarial Opus review found + fixed: the mana-meter orphan (A2 left unhidden)
and the meter tile-vs-cap render bug (C1). Divergence rows AP-46 (health gate
approximation: IsLiveCreatureTarget vs IsPlayer||pet||attackable) + AP-47
(meter shown on select vs on UpdateHealth reply). Spec §5 corrected.

Build + full test suite green (2,684 passed / 4 skipped). Health meter render
fidelity (full-width fill + fraction mapping) pending the user's visual gate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.Core.Net/WorldSession.cs

@@ -1140,6 +1140,18 @@ public sealed class WorldSession : IDisposable
         SendGameAction(body);
     }
 
+    /// <summary>Send retail QueryHealth (0x01BF). Server replies UpdateHealth (0x01C0).</summary>
+    /// <remarks>
+    /// Retail anchor: <c>CM_Combat::Event_QueryHealth</c> / <c>gmToolbarUI::HandleSelectionChanged:198635</c>
+    /// (docs/research/named-retail/acclient_2013_pseudo_c.txt).
+    /// </remarks>
+    public void SendQueryHealth(uint targetGuid)
+    {
+        uint seq = NextGameActionSequence();
+        byte[] body = SocialActions.BuildQueryHealth(seq, targetGuid);
+        SendGameAction(body);
+    }
+
     /// <summary>Send retail TargetedMeleeAttack (0x0008).</summary>
     public void SendMeleeAttack(uint targetGuid, AttackHeight attackHeight, float powerLevel)
     {